The cost of outboard motors has increased at an alarming rate. The average yearly price increase over the last ten years has been 6.5% with an 11.5% increase attributable to 2005 alone. An outboard motor can account for over 60% of the cost of a boat/motor/trailer package. This high cost has become a serious hindrance to attracting new customers to the recreational activity of boating.
It is well known in the field of marine propulsion that it is advantageous to use engines designed and manufactured for use in other, higher volume industries. For example, gasoline engines from the automotive industry are the predominant power source to the marine industry for small to mid-size vessels that rely upon stern drives and inboards. The primary power source for larger vessels is diesel engines adapted for use from the trucking industry.
While engines from the automotive and trucking industry provide cost advantages over custom built engines, such as outboard motors, the adaptation still requires the use of customized cooling systems and other modifications that can be most expensive.
Any time an engine designed for another industry is adapted for use in the Marine environment; there are design barriers which must be overcome. For instance, automobile engines corrode when exposed to salt water found in oceans. So closed cooling systems are often added to protect the iron engine blocks.
Further, since engines designed for other industries are not anticipated to be installed in a boat, one must find a way to make such installation simple and cost effective.
The lowest cost engines in the world, on a $/hp basis, come from the L&G (Lawn and Garden) industry. Unfortunately these engines are not designed to be used in boats.
The idle rpm of L&G engines are unacceptable for a marine application, often approaching 1,800 rpm when a conventional outboard motor would be expected to idle at less than 1,000 rpm.
Finally, L&G engines that are the most cost effective are air cooled. So one must find ways to bring cool air into the lawn and garden engine and dispose of that hot air in a safe and cost effective manner.
U.S. Pat. No. 3,164,122 by Fageol discloses a transom mounted propulsion assembly. Fageol does not employ commonly available motors or rudder systems.
U.S. Pat. No. 2,976,836 by Fageol discloses a vertical shaft inboard marine power plant wherein the drive assembly is in combination with the rudder. The engine and drive assembly are secured by a ball and socket assembly wherein the propeller is moved to cause directional steering of the vessel.
U.S. Pat. No. 4,907,994 by Jones discloses a drive system for a vessel wherein the propeller is moved to cause directional steering of the vessel.
U.S. Pat. No. 5,108,325 by Livingston discloses a drive system for a vessel wherein the propeller is moved to cause directional steering of the vessel, and further allows elevated movement of the propeller.
U.S. Pat. No. 5,326,294 by Schoel discloses a stern drive system for a vessel wherein the propeller and rudder are moved to cause directional steering of the vessel.
One of the problems with the prior art is the movement of the propeller induces inefficiencies in operation by changing the flow characteristics as well as inducing unpredictable flow currents in relation to the hull.
Thus, what is needed in the marine industry is a low cost mass produced engine from the lawn and garden industry that provides the performance, installation ease, idle quality and reliability of an outboard motor, without the associated specialty motor expense.